Analysis of the effect of both specimen size and grain size on the tensile strength of the polycrystalline metallic materials

摘要

A modified strain gradient plasticity theory is proposed based on the mechanism-based strain gradient (MSG) plasticity. This study is motivated by nonhomogeneity of polycrystalline materials. We believe that the geometrically necessary dislocations (GND) are generated on slip system as well as grain boundary to accommodate the deformation shape with internal stress. The new theory differs from the MSG plasticity in consideration of the GND on grain boundary and free surface effect of polycrystalline materials. A model describing the size effect on the tensile strength of crystalline metallic materials is investigated. Using the nonhomogeneity of polycrystalline materials and free surface effect, the density of the geometrically necessary dislocations during tension is derived. Using the proposed model, an analysis of the effect of both specimen size and grain size on the tensile strength of the polycrystalline materials is carried out.